The present invention relates to grinding apparatus for defiberating cellulosic material in the space between two opposed, relatively rotating grinding disks. More particularly, this invention relates to an improved bearing assembly for mounting about the rotating shaft such a grinding apparatus.
Such grinding apparatus, typically termed refiners, may be used to defiberize or disintegrate various cellulosic materials. However, one very common use of such refiners is to mechanically defiberize wood chips to produce pulp for use in making paper. Although this treatment may be carried out in a number of different ways, the refining process generally involves separating and cutting the fibers of the wood chips by passing the wood chips between spaced grinding surfaces commonly referred to as discs. More particularly, two parallel discs are disposed in spaced relationship and rotate one relative to the other. The surface of the discs have refiner plates mounted thereto which provide a surface for acting upon the wood chips in the gap defined therebetween.
In the refining process, it is often necessary to optimize the process by adjusting the gap between the refiner plates in response to changes in the nature of the wood chips being processed, the consistency of the pulp slurry forming between the plates, the operating load on the refiner, and other known factors. Additionally, it is sometimes necessary to adjust the spacing between the plates in order to avoid undesirable contact between the plate surfaces known as plate clashing. Such plate clashing can destroy the surface configuration of the plates which typically are designed with a specific and concise configuration of grooves and bars.
In order to adjust the gap between the opposed plate surfaces, it is customary to axially displace one of the grinding discs with respect to the other. This typically involves axially translating the entire shaft together with the discs mounted thereto within its housing. Of necessity, the bearing supporting the shaft must also translate with the shaft within the housing. Therefore, it is necessary to design the bearing assembly such that axial movement is permitted between the bearing retainer ring and the bearing housing structure. In typical prior art bearing assemblies, the bearing retainer ring is typically held in place within the bearing housing by a cylindrical loose fit and key/keyway-type structure to prevent rotation. An axially elongated key is mounted to extend outwardly from the retainer ring and loosely mate into a corresponding keyway formed in the bearing housing structure. A loose fit must be provided between the retainer and the bearing housing and in key to keyway mounting so as to permit axial translation of the retainer ring as the shaft is moved within the housing. Unfortunately, the requirement for such a loose fit reduces the horizontal stiffness of the structure making it difficult to control shaft vibration which in turn can result in wear between the mating parts necessitating shutdown of the machinery for the replacement of prematurely worn parts.